The present invention relates to apparatus and method for measuring balance and force variation on a rotating object and, more particularly to a combination of the two types of measurement on a force variation measurement machine for a pneumatic tire.
In the art of manufacturing pneumatic tires, rubber flow in the tire mold or minor differences in the dimensions of the belts, beads, liners, treads, plies of rubberized cords, etc., sometimes cause non-uniformities in the final tire. Non-uniformities of sufficient amplitude will cause force variations on a surface, such as a road, against which the tires roll producing vibration and noise. When such force variations exceed an acceptable maximum level, the ride and handling of a vehicle utilizing such tires will be adversely affected. It is known that the magnitudes of the force variations change with the speed of tire rotation, generally (but not always) increasing in magnitude with speed, therefore a vehicle operator""s perception of tire quality (and vehicle ride) will be most influenced by the force variations occurring at high speeds such as xe2x80x9chighway speedsxe2x80x9d of, for example, 100 kilometers per hour (kph) and higher. Accordingly, purchasers of tires, especially large volume purchasers such as vehicle manufacturers (xe2x80x9cOEMsxe2x80x9d), would prefer to know and specify maximums for high speed force variations on purchased tires. Unfortunately, direct measurement of high speed force variations on tires is difficult and expensive, therefore the industry has devised a variety of equipment and methods for predicting high speed tire performance (uniformity, force variations) based on statistical sampling and on simpler measurements primarily including xe2x80x9clow speedxe2x80x9d tire uniformity measurements, and possibly also measurements of tire balance. Also, it is increasingly common for purchasers to request tire balance information. Thus, for a variety of reasons, it has become necessary to measure both force variation and balance on pneumatic tires inline with the tire manufacturing process.
During the typical tire manufacturing process, factory floor measurements of tire uniformity are performed on force variation machines (xe2x80x9cFVMxe2x80x9d), also known as tire uniformity machines (xe2x80x9cTUMxe2x80x9d) which are used to monitor the quality of the tire production process and may guide or incorporate corrective measures such as grinding to improve the balance and uniformity of a tire. A factory floor, production FVM is a low speed unit, typically operated at 60 rpm (revolutions per minute) which only corresponds to about 6 miles per hour (10 kph) for a typical passenger car tire. In general, a tire uniformity machine subjects a tire to normal conditions of mounting, inflation, load and rotation (at low speed) while collecting measurement data on variations of force, and sometimes also runout, and angular velocity. A force variation machine typically includes an assembly for rotating a test tire against the surface of a freely rotating loading wheel. In such an arrangement, the loading wheel is acted upon in a manner dependent on the forces exerted by the rotating tire and those forces are measured by appropriately placed measuring devices, connected to supporting structure of the loading wheel. Many production force variation machines are equipped with grinders, so that when a tire being tested yields unacceptable results, shoulder and center rib grinders can be used to remove a small amount of the tire tread at precisely the location of non-uniformities detected by the measuring devices. As the tire is rotated, it is measured and ground simultaneously. In a sophisticated, low speed production tire uniformity machine, such as a Model No. D70LTX available from the Akron Standard Co. of Akron Ohio, the force measurements are interpreted by a computer and rubber is removed from the tire tread using grinders controlled by the computer. In modern, automated production facilities, tires are conveyed to and from fully automated force variation machines that can complete force variation measurements in approximately 30 seconds.
If balance measurements are desired, then after undergoing measurement, and optionally correction, of force variations in a FVM/TUM, the tire must be removed from the FVM and placed into a separate balance machine to measure the amount of imbalance of the tire. Typically, the tires are mounted in the balance machine in a manner similar to that of the tire uniformity machine and inflated to a preset pressure. Then, the static (single-plain) and couple (two-plain) imbalances are measured by one of a variety of well-known methods. A separate balance machine is used because balance is measured by sensors mounted on the spindle about which the tire rotates. There is no loading wheel, and the tire rotates at a high speed, such as 380 rpm.
The measurement of balance on every tire given force variation measurement in production would require a large expenditure of capital to add hundreds of balance machines. Furthermore, balance measurement requires added manpower, added conveyors, added factory floor space, added energy, and importantly increased production time as a tire on the FVM is slowed and stopped, deflated, removed from the rim, conveyed to the balance machine, re-mounted on a rim, re-inflated, and accelerated to measurement speed. Even further, if correlation of force variation and balance measurements is desired, then the tires must be marked with an index mark to show a rotational zero-degree point, and both the FVM and balance machine must be capable of detecting the index mark.
In order to solve these and other problems, thereby improving productivity and reducing costs, it is an object of the present invention to provide method and apparatus that enables automated measurement of both balance and force variation on a single machine, preferably by modifying existing FVM/TUM equipment.
According to the invention, there is disclosed a machine for measuring both force variation and balance for a pneumatic tire. The machine comprises a top spindle rotatably held in a top spindle housing, a top flange affixed at the bottom of the top spindle, and a bottom flange located at the top of a bottom spindle, the top and bottom flanges being matable for locking the flanges together with the tire sealingly mounted therebetween. Rotating means are provided for turning the top spindle to rotate the tire at a low speed for force variation measurements and at a high speed for balance measurements. Disconnecting means the rotating means from the top spindle enables free rotation of the top spindle. Assembly means for disconnecting the bottom flange from the bottom spindle enables free rotation of the bottom flange. First sensors mounted to a load wheel measure force variations when the tire is rotated while loaded by the load wheel. Second sensors mounted on the top spindle housing measure tire balance when the tire is not loaded by the load wheel and is rotating on a freely rotating top spindle and a freely rotating bottom flange.
Also according to the invention, the assembly means is a cone assembly comprising: an annular spindle cone ring encircling and attached to the top of the bottom spindle; an annular flange cone ring surrounding the spindle cone ring and attached to the bottom flange; and the spindle cone ring having a frustraconical radially outward surface that slants radially inward from bottom to top which mates with a frustraconical radially inward surface of the flange cone ring that slants radially inward from bottom to top at the same angle as the spindle cone ring outward surface.
Also according to the invention, a removal ring is attached above the spindle cone ring on the bottom spindle, the removal ring having a circumferential hook lip that extends radially outward from a top portion of the removal ring, for pulling the bottom flange downward and out of engagement with the tire.
Further according to the invention, a lock mechanism is engaged to hold the bottom spindle in a measurement position such that the cone assembly disconnects the bottom flange from the bottom spindle.
Still further according to the invention, an encoder determines the rotational angle of the tire.
Also according to the invention, a controller is programmed to calculate tire balance, to correlate tire balance and force variation data, and to use a combination of tire balance and force variation data to control tire uniformity corrections. The controller 62 includes means to control the elevation of the bottom spindle for disconnecting the cone assembly during balance and force variation measurements; means to control the rotating means to accelerate tire rotation to the high speed and then to disconnect the rotating means from the top spindle for measuring tire balance; means to control the reconnect the rotating means to the top spindle after measuring tire balance, and then to decelerate tire rotation; and means to calculate tire balance.
Still further according to the invention, a brake mechanism is provided for stopping rotation of the top spindle.
Further according to the invention, the second sensors comprise four single axis load cells, two sensors being mounted on either side of an upper portion of the top spindle housing, and two sensors being mounted on either side of a lower portion of the top spindle housing.
According to the present invention, there is provided a modification kit for adding balance measurement capability to a force variation machine for pneumatic tires; the force variation machine including vertically mounted top and bottom spindles with a top flange affixed at the bottom of the top spindle and a bottom flange located at the top of the bottom spindle, the flanges being mateable for locking the flanges together with the tire sealingly mounted therebetween; a loading wheel with first sensors for measuring force variations when the tire is rotated while loaded by the load wheel; and tire rotating means connected for rotating the top spindle. The modification kit comprises a top spindle housing rotatably holding the top spindle and having second sensors for measuring tire balance; and an assembly for disconnecting the bottom flange from the bottom spindle.
Further according to the invention, the modification kit comprises bearings between the top spindle and the top spindle housing suitable for balance measurements made by the second sensors. The assembly is a cone assembly comprising an annular spindle cone ring encircling and attached to the top of the bottom spindle; an annular flange cone ring surrounding the spindle cone ring and attached to the bottom flange; and the spindle cone ring having a frustraconical radially outward surface that slants radially inward from bottom to top which mates with a frustraconical radially inward surface of the flange cone ring that slants radially inward from bottom to top at the same angle as the spindle cone ring outward surface; a motor for turning the top spindle to rotate the tire at a low speed for force variation measurements, and for rotating the tire at a high speed for balance measurements; a clutch for disconnecting the motor from the top spindle; and a rotary air coupling interfacing a non-rotating air line with the bottom flange.
Still further according to the invention, the modification kit comprises a removal ring attached above the spindle cone ring on the bottom spindle, the removal ring having a circumferential hook lip that extends radially outward from a top portion of the removal ring, for pulling the bottom flange downward and out of engagement with the tire.
Yet further according to the invention, the modification kit comprises an encoder for determining the rotational angle of the tire; controller means to control the elevation of the bottom spindle for disconnecting the cone assembly during balance and force variation measurements; means for controlling the motor and clutch whereby the motor can be connected to the top spindle to accelerate tire rotation to the high speed and the motor can be disconnected from the top spindle for measuring tire balance; means for controlling the motor and clutch whereby the motor can be connected to the top spindle after measuring tire balance to slow down the tire rotation; and means for calculating tire balance.
According to the present invention, there is provided a method for determining both force variation and balance of a pneumatic tire on a single machine. The method comprises the steps of: mounting the tire between a top flange on a top spindle and a bottom flange on a bottom spindle of the machine; mating the bottom flange with the top flange and disconnecting the bottom flange from the bottom spindle; inflating the tire; engaging the tire with a load wheel; rotating the top spindle at a first speed and measure forces on the loading wheel to determine tire force variation; and rotating the top spindle at a second speed and measure forces on the top spindle to determine tire balance when the load wheel is disengaged from the tire.
Still further, according to the present invention, there is provided a method wherein the step of rotating the top spindle at the second speed includes disconnect a rotating means from the top spindle after the tire rotation has reached the high speed before measuring forces on the top spindle.
Also according to the present invention, the method further comprises the steps of: connecting the bottom flange to the bottom spindle with compressive forces; and disconnecting the bottom flange from the bottom spindle with tensile forces; and pulling the bottom flange away from the top flange by a moving bottom spindle.
Further, according to the present invention, the first speed is between 20 rpm and 130 rpm, and the second speed is between 200 rpm and 600 rpm.
Still further, according to the present invention, the first speed is preferably between 50 to 70 rpm, and the second speed is preferably between 350 to 400 rpm.
Also, according to the present invention, the method further comprises the step of correlating tire balance and force variation data.
Still further, according to the present invention, the method comprises the step of controlling tire uniformity corrections using a combination of tire balance and force variation data.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.